In the context of internal combustion engines (ICEs), the technique of altering the timing of a valve lift event is commonly referred to as variable valve timing (VVT). Use of such design is known in the art in order to, inter alia, improve upon the performance, fuel economy, or reduce the emissions of an internal combustion engine to which it is applied. Especially in the automotive industry, increasingly strict environmental regulations are causing countless manufacturers to modify the relative timing, duration, or opening of their engines' inlet and exhaust valves.
Among several approaches to variable valve timing known to the skilled person, so-called cam phasing allows to change the phase of the camshaft's and valves' periodic movement. To this end, the camshaft is rotated relatively to the crankshaft. When compared to a fixed camshaft, cam phasing not only enables an internal combustion engine to deliver high power, but also to work tractably and efficiently at low power.
Conventional apparatus for cam phasing comprises an electronically controlled hydraulic valve called an oil control valve (OCV). The hydraulic valve is designed as a multiple-port, multiple-position valve in cartridge construction. Non-return check valves, which are designed as band-shape rings, are inserted on the inside of the snout or central bolt. By means of these non-return check valves, camshaft alternating torques are utilized in order to assist camshaft adjustment more rapidly and with a relatively low oil pressure. For this purpose, check valves open to utilize pressure peaks as a consequence of camshaft alternating torques and cover the openings to prevent back flow into the lower pressure port.
In a typical implementation, a powertrain control module (PCM) may transmit a signal to an associated solenoid to move a spool of this hydraulic valve, thereby regulating the flow of oil to the cavity. This allows for the camshaft to be slightly rotated from its initial orientation, serving to advance or retard the resulting timing. Besides other criteria, the powertrain control module may control the camshaft timing depending on a current load on the engine or frequency of its rotation.